<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>圆</title>
</head>
<body>



<input type="text" placeholder="半径" id="a">
<br>
<input type="text" placeholder="周长" id="b">
<br>
<input type="text" placeholder="面积" id="c">





<script>

    var r = prompt("");
    var p = Math.PI;
    console.log(p);

    r = parseInt(r);

    document.querySelector("#a").value = r;
    document.querySelector("#b").value = 2*r*p;
    document.querySelector("#c").value = r*r*p;

</script>




</body>
</html>